This application contains subject matter also contained in copending application Ser. No. 09/426,650.
This invention relates generally to circuit breakers and more particularly to current responsive circuit breakers for interrupting electrical circuits on the occurrence of predetermined overload conditions in the circuits.
Current responsive electrical circuit breakers typically interrupt electrical circuits in response to the occurrence of selected overload current conditions in the circuits to protect other equipment and wiring in the circuits from damage due to overheating or overcurrent or the like. In one particularly advantageous circuit breaker shown in U.S. Patent No. 3,361,882 commonly assigned to the assignee of the present invention, the disclosure of which is included herein by this reference, an actuator mechanism manually moves movable contacts into and out of engagement with complementary stationary contacts to make and break a circuit. A current carrying thermostatic trip member is operable to break the circuit in response to the occurrence of a selected overload current in the circuit. The thermostatic trip member is a composite member having a metal layer formed of relatively higher coefficient of expansion and a co-extensive metal layer formed of relatively lower coefficient of expansion arranged so that the layer having the lower coefficient of expansion faces a motion transfer member which is slidably positioned between a portion of the thermostatic trip member which moves with changes in temperature of the thermostatic trip member and a catch assembly. The catch assembly includes a catch surface which interacts with a latch attached to the actuator mechanism. Upon overcurrent conditions the current carrying thermostatic trip member bends thereby moving the motion transfer member which in turn moves the catch assembly releasing the latch to allow the actuator mechanism to move the movable contact and break the circuit. The catch assembly includes a compensator formed of thermostatic material having a layer of relatively higher coefficient of expansion and a layer of relatively lower coefficient of expansion. The compensator is generally U-shaped, having first and second legs extending from a bight with the ends of the legs fixedly attached to a cross-bar of a T-shaped member which extends upwardly between the legs and with the top surface thereof serving as the catch for the latch of the actuator mechanism. The cross-bar is mounted for pivotal motion and is biased toward a normal operating position. The compensator is arranged so that the side having the higher coefficient of expansion faces the trip member. The bight of the U-shaped compensator which is aligned with the motion transfer member moves in the same direction that the trip member moves with changes in temperature to reduce the effect of ambient temperature changes, or in other words, to make the circuit breaker less sensitive to changes in ambient temperature. Thus, the distance between the trip member and the compensator at the location of the motion transfer member stays relatively constant with changes in ambient temperature however, as mentioned above, upon sufficient heating of the trip member due to overcurrent conditions, the trip member will bend toward the compensator causing the motion transfer member to move and the compensator to pivot along with the catch and thereby release the latch to break the circuit.
There are applications, however, in which there is a need to increase sensitivity to ambient temperature changes, at least over a selected range of ambient temperature.
It is an object of the present invention to provide a circuit breaker which has increased sensitivity to changes in ambient temperature. Another object of the invention is to provide a circuit breaker which has increased sensitivity to changes in ambient temperature at elevated temperatures and with higher trip temperatures and forces of the current carrying tip member. Still another object is the provision of a circuit breaker which has a lengthened overload trip time at room temperature. Another object of the invention is the provision of a circuit breaker in which the ultimate trip current is increased with a decrease in ambient temperature. Still another object of the invention is the provision of a circuit breaker in which one type of ambient temperature sensitivity can be selected over a first portion of a temperature range and a second, different type of ambient temperature sensitivity can be selected over a second portion of the temperature range.
Briefly, in accordance with a first embodiment of the invention, an ambient temperature adjustment member, formed of thermostatic material having a layer of relatively higher coefficient of expansion material and a layer of relatively lower coefficient of expansion material, is oriented so that it reacts to temperature in a direction that is opposite to the direction that a current carrying thermostatic trip member moves in reaction to changes in temperature thereby decreasing the distance between the trip member and the compensator when both are heated and making the circuit breaker sensitive to increases in ambient temperature. In a modified embodiment a compensator stop element is mounted in fixed relation to the catch and positioned to limit motion of the adjustment member at a selected location with decreasing ambient temperature thereby providing a circuit breaker which is sensitive to increased ambient temperature without decreasing the room temperature trip temperature of the trip member. In accordance with another embodiment of the invention, the adjustment member is separated at the bight and the first and second legs are formed of materials different from one another to provide various responses to changes in ambient temperature including ambient compensation and non-compensation of various degrees in two separate temperature ranges. The materials which can be used for the first and second legs include any desired combination of thermostatic members with more or less thermally responsive motion and with forward or reverse motion as well as thermostatic and non-thermostatic members.